Content area
Abstract
Introduction and objective
The 2030 Immunization Agenda envisions a global landscape where everyone can equally access the benefits of both new and existing vaccines by expanding equitable coverage. Post-introduction evaluation strategies are essential to ensure efficient and rational use of resources invested in immunization programs. However, a notable gap remains in the literature on how these strategies are applied in low- and middle-income countries. This study identify the main strategies used worldwide to monitor vaccines after their incorporation into immunization programs.
Methods
This systematic literature review was conducted in accordance with the Cochrane Handbook for Systematic Reviews of Interventions and reported following PRISMA guidelines. Studies were retrieved from PubMed (MEDLINE), Web of Science, Core Collection, SCOPUS, and EMBASE (Elsevier) databases. The review included studies on vaccine monitoring after incorporation into immunization programs, with no date restrictions. Excluded were narrative and systematic reviews, meta-analyses, letters, book chapters, posters, COVID-19 vaccine studies, non-human vaccination research, and studies assessing general impact without post-introduction monitoring.
Results
The search identified 4812 citations, with 1477 duplicates removed. After screening 3335 titles and abstracts, nine studies met the inclusion criteria. While the concept of post-introduction monitoring strategies remains poorly defined, the studies revealed that such monitoring can be performed through evaluation of surveillance systems, economic assessments, and adapted analytical tools. Sentinel surveillance, involving healthcare workers and services, was the most frequently reported strategy, followed by synthetic control methods, pre- and post-introduction comparisons, and use of a World Health Organization tool.
Conclusions
Despite the absence of a standardized framework for post-introduction vaccine monitoring, existing studies demonstrate that evaluations can address effectiveness, safety, coverage, and cost. Beyond epidemiological significance, the incorporation of vaccines into immunization programs provides an opportunity to strengthen policies, promote workforce development, and foster social mobilization in support of vaccination.
Full text
1 Introduction
Immunization is one of the most cost-effective interventions for preventing and controlling potentially fatal infectious diseases [ 1]. Reducing vaccine-preventable infections is an essential pillar of public health, as these diseases impose a high burden of morbidity and mortality and costs on health systems [ 2–4]. Reducing them is essential for strengthening public health actions, as they directly impact mortality, quality of life, and social productivity, in addition to reducing long-term costs [ 3, 4].,
The 2030 Global Immunization Agenda (IA2030) [ 2] seeks to establish a world where everyone, regardless of location, can fully benefit from both newly developed and existing vaccines [ 5] through expanded equitable access [ 5]. Between 2001 and 2020, efforts focused on introducing new vaccines and increasing coverage averted an estimated 350 million cases of new infectious diseases, prevented 8 million instances of long-term disability, and saved approximately 14 million lives [ 3].
Following the decision to add a new vaccine to the national immunization schedule, post-introduction evaluations often remain limited to initial coverage rates, overlooking critical factors such as real-world vaccine effectiveness, equitable access, public acceptance, and adverse events [ 6, 7]. Despite the existence of standardized approach for conducting post-introduction evaluations, adherence is suboptimal, thereby limiting the ability to generate evidence necessary for technical and operational improvements [ 8]. Studies assessing the incidence of vaccine-preventable diseases following vaccine implementation have underscored the critical role of such evaluations in promoting immunization efforts and supporting the achievement of high vaccination coverage [ 4, 9, 10].
The integration of new vaccines into National Immunization Programs represents a major step forward in preventing infectious diseases. However, it demands systematic, continuous evaluation to accurately gauge its public health [ 11] impact. Post-introduction assessments are essential for ensuring the efficient use of immunization resources, addressing vaccine hesitancy, improving program transparency, and supporting evidence-based responses to potential adverse events [ 11–15].
The World Health Organization (WHO) recommends that countries conduct a post-incorporation evaluation between 6 and 12 months after the rollout of a new vaccine to assess its implementation and adopt necessary corrective actions [ 13]. Therefore, in-depth studies of evaluation methods, field experiences, and lessons learned are essential to expand the evidence base and inform future assessments. A key strategy within the global immunization agenda is the strengthening of monitoring and evaluation at both national and subnational levels to enhance accountability and support the achievement of immunization targets [ 16, 17].
Currently, despite the availability of standardized protocols for conducting post-introduction assessments, the rate of adherence to these guidelines remains insufficient compared to what is recommended [ 18] - particularly in low- and middle-income countries. Most of the existing literature is concentrated in developed countries, representing a gap in the evaluation of heterogeneous scenarios with different surveillance and monitoring structures [ 19].
In the United Kingdom and the United States, for example, studies are conducted using clinical and hospital databases, while low-income countries resort to periodic population surveys with sample surveys to estimate coverage [ 8, 20]. Canada and the United Kingdom use integrated records for real-time analysis, while Latin American countries rely on vaccination coverage surveys [ 8, 18].
This regional disparity compromises understanding of the challenges faced in contexts with less surveillance capacity, which makes it important to expand and adapt standardized strategies for post-vaccine introduction monitoring and evaluation. To overcome these limitations, it is essential to ensure that post-incorporation evaluations of vaccines are equitable and comparable across different contexts, in order to strengthen vaccination policies that are best suited to local realities.
Moreover, this gap underscores the fragility of the management systems responsible for long-term vaccine monitoring. While countries with well-established infrastructures implement ongoing post-marketing surveillance, periodic economic evaluations, and large-scale assessments of effectiveness and safety, many others lack the necessary tools to systematize this process [ 20].
Gaining insight into the strategies employed globally for the post-introduction phase of new vaccines is critical to informing evidence-based recommendations for immunization programs. Furthermore, examining these strategies can guide future decision-making processes, including the potential expansion of target age groups, adjustments to dosing schedules, or the removal of less effective vaccines from national immunization programs.
This study set out to identify the main strategies used for the monitoring the incorporation of vaccines into national immunization programs through a systematic review of the existing literature.
2 Methods
This systematic literature review was conducted in accordance with the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions [ 21] and reported in line with the PRISMA [ 22] guidelines. The review protocol was registered in the PROSPERO database under the identifier CRD42025637594.
The guiding research question for this review was: ‘What are the main strategies for monitoring the incorporation of vaccines into immunization programs worldwide?’ To construct the research strategy, the PCC (Population–Concept–Context) framework was applied [ 23]. For the ‘P' component (Population), the general population was considered without specific demographic restrictions. The ‘C' representing the Concept was addressed through descriptors related to monitoring strategies, while the second ‘C' (Context) incorporated descriptors on vaccination and immunization programs.
2.1 Search strategy
The search strategy was implemented using PCC terms adapted for the databases PubMed (MEDLINE), Web of Science Core Collection, SCOPUS, and EMBASE (Elsevier) (see Supplementary Table 1). When available as indexing terms (MeSH or Emtree), the PCC descriptors were used alongside text words in PubMed and EMBASE databases [ 23]. Only text-word terms were used for the Web of Science Core Collection and SCOPUS databases. These text words were not restricted to titles or abstracts but were applied broadly to maximize coverage. Searches were conducted without limitations on location, period, or language in January 2025 and updated in May 2025. Synonymous search terms were combined using the Boolean operator ‘OR’, while the groups of synonymous terms corresponding to each PCC component were combined using ‘AND’.
2.2 Eligibility criteria
Studies addressing aspects of vaccine monitoring following their introduction into immunization programs worldwide were included, with no restrictions on time period. The exclusion criteria were: (1) Narrative and systematic reviews, as well as meta-analyses; (2) Letters to the editor; (3) Book chapters; (4) Poster presentations; (5) Studies on the monitoring of COVID-19 vaccine introduction; (6) Research not focused on human vaccination; and (7) Studies addressing general vaccine impact or effectiveness without the specific objective of evaluating the post-introduction monitoring framework. Monitoring of COVID-19 vaccine incorporation was excluded from this review due to the atypical pandemic context, which could lead to methodological bias. Moreover, duplicate studies, unretrieved studies, those that did not discuss post-introduction vaccine evaluation strategies, and one study in Persian language were removed. The PRISMA flow diagram, detailing the inclusions and exclusions of studies for this review, can be found in
Fig. 1
2.3 Data selection and extraction
Titles and abstracts identified through the search were independently screened by two reviewers using the Rayyan® platform. Studies meeting the inclusion criteria underwent full-text screening. Any discrepancies were resolved through consensus, and when disagreements persisted, a third and fourth reviewer were involved. Articles that met the eligibility criteria were subsequently included in the review.
Due to the expected heterogeneity across the included studies, both in terms of methodological design and the monitoring strategies adopted, data synthesis was conducted using the Synthesis Without Meta-analysis (SWiM) guidelines [ 25]. Accordingly, data extraction was performed by the same four reviewers. The extracted information was then organized into narrative comparative tables, highlighting the main characteristics, assessed attributes, reported limitations, and resulting recommendations.
2.4 Methodological quality assessment
The assessment of the methodological quality of the studies was conducted independently by two researchers using the Newcastle-Ottawa Scale [ 24]. The studies were evaluated based on the following domains: (i) selection (0–4 points); (ii) comparability (0–2 points); and (iii) outcome assessment (0–3 points), resulting in a total score of 9 points. Four studies scored 7 points, one study scored 8 points, and four studies scored 9 points. The methodological quality of each of the studies can be found in Table 3.
2.5 Data analysis
The data were grouped by narrative synthesis, and the results were formatted into descriptive tables using the SWiM methodology. The SWiM guideline has a nine-item checklist to promote transparent reporting: (1) Grouping of studies for synthesis (2) Description of the standardized metric and transformation methods used (3) Description of synthesis methods (4) Criteria used to prioritize results for summary and synthesis (5) Investigation of heterogeneity in reported effects (6) Certainty of evidence (7) Methods of data presentation (8) Reporting of results (9) Limitations of the synthesis [ 25].
As for the qualitative content analysis, the examination of the material was conducted through thematic coding, in which meaningful excerpts from the narratives were identified and grouped based on content similarities: Surveillance of morbidity and mortality; surveillance of disease-related complications/hospitalizations; surveillance of new cases of the disease; quality of life; surveillance of adverse events; surveillance and monitoring of administered doses; vaccination logistics; professional training; vaccine acceptance and monitoring strategies (with the following subcategories: sentinel surveillance, retrospective post-incorporation evaluation). It is important to note that, since the categories and subcategories are empirical and therefore surfaced directly from the material, some relevant topics to post-introduction evaluation, such as vaccine financing, were not included as categories because they were not explored in the studies. The coding process was supported by the MAXQDA24® software.
3 Results
The search strategy retrieved 4812 citations, of which 1477 were removed due to duplication. Thus, 3335 titles and abstracts were evaluated. Finally, nine [ 26–34] studies were included in this systematic review ( Fig. 1).
The vaccines addressed in the nine studies were: human papillomavirus (HPV) vaccine, rotavirus vaccine, varicella vaccine, pentavalent vaccine, pneumococcal conjugate vaccine, poliomyelitis vaccine, and malaria vaccine. Particular attention was given to the rotavirus vaccine, which was examined in two of the nine included studies (A2 and A8). Regarding geographic focus, states and countries in Asia were prominent, with three studies conducted in this region (A2, A5, and A8). Brazil was the setting for one study, conducted in collaboration with Chile, Ecuador, Mexico, and the United States (A6). One study included in this review did not aim to evaluate a specific vaccine (A4), but rather sought to explore the relevance of conducting retrospective analyses following the introduction of vaccines into health systems. This approach allowed for a discussion of methodological challenges in supporting decision-making, regardless of the vaccine (
Table 1
Table 2
Studies A1, A2, A3, A5, and A8 underscored the critical role of ongoing surveillance, highlighting the necessity of robust systems—such as sentinel networks, national registries, and structured questionnaires—to track both vaccine coverage and safety. Complementary mechanisms were also noted, including cancer registries in the United States, nationwide surveys in Canada, and active surveillance initiatives in India).
Regarding challenges in implementing these strategies, studies reported issues such as data inconsistencies (A5, A8); logistical difficulties in managing services, including recruiting and retaining staff and sentinel sites, as well as coordinating with researchers; and incorrect completion of data collection forms (A9). Other challenges included public perception of the disease targeted by the vaccine as a significant health problem (A2) and limited financial resources (A2, A5). Positive factors highlighted in multiple studies included community engagement, professional training (A5, A7), and the use of data collected during post-introduction evaluations to inform rapid policy adjustments and identify weaknesses in vaccination programs and health systems (A4, A6).
3.1 Dimensions of the evaluation of the introduction of new vaccines in the vaccination schedule of immunization programs (Epidemiological, Economic, Operational, and Social/Behavioral)
The articles demonstrated that the introduction of new vaccines into the vaccination schedule of immunization programs can be investigated through the evaluation of four dimensions: E
pidemiological, Economic, Operational, and Social/Behavioral.
Fig. 2
In the Epidemiological dimension, the two main aspects were the evaluation of the efficacy and safety of the vaccines. To evaluate efficacy, the main consideration was the monitoring of new cases of vaccine-preventable diseases (A1, A2, A3, A9, A7, A6), comparing the incidence of new cases before and after introduction in the short and medium term. In addition to new cases, the incidence of complications/hospitalizations and mortality was evaluated (A1, A2, A9, A7, A6). To define the cases of illness and complications caused by the diseases, the studies used clinical investigation methods (clinical diagnosis, signs, and symptoms) (A1, A2, A3, A9, A6) and laboratory criteria with serotype identification (A2, A3, A9, A6). The studies also assessed the epidemiological burden of vaccine-preventable diseases (A2, A9), as well as the progress in reducing the circulation of pathogens responsible for vaccine-preventable diseases, and consequently, their elimination and eradication (A2, A9, A6). Regarding safety assessment, the studies used the monitoring of Adverse Events as a measure, based on national data (A3, A8) and specific national initiatives (A3).
Moreover, in the Operational dimension, the studies discuss vaccination logistics considering the cold chain network (including availability, storage, inventory, transportation, and disposal of doses) (A5, A4), vaccination guidelines (A4), professional overload (A5), investigation of community subgroups and microplanning of actions (A5), formation of committees for vaccination actions (A5), and intersectoral coordination (A4). Moreover, an important aspect considered was the monitoring of vaccination coverage and doses administered (A1, A2, A3, A8, A9, A5, A4, A6). In this way, the need to train healthcare professionals to promote the delivery of vaccination with safety, efficacy, and community trust is emphasized. For this, professionals must have theoretical-practical knowledge about the incorporated vaccine, its administration, calculation of vaccination coverage, dropout rate, dose wastage, among others (A5, A4).
In the Social/Behavioral dimension, mobilization and social communication actions for the defense and promotion of vaccination are valid, such as the promotion and distribution of educational materials about the new vaccine (A8, A5), strengthening communication between health professionals and the community (A8), disseminating information through media (radio, television, strategic information points, and mobile units) (A8, A5), and training community representatives (A5). Furthermore, the acceptance and refusal of vaccines by the community (A8, A5, A4), caregivers and guardians of children, and healthcare workers (A5) were evaluated.
Finally, in the Economic dimension, although the economic aspects were not deeply explored in the articles, some studies addressed the costs of vaccine production, research, development, and their introduction into the vaccination schedule (A9), as well as the requirement for funding for such (A4) and the reduction of expenses for the population that previously had to pay for vaccines in the private healthcare system (A4).
3.2 Post-introduction evaluation strategies
Based on the coding analysis of the material into empirical categories, it was possible to construct a conceptual map of strategies for monitoring the integration of vaccines into immunization schedules (
Fig. 3
One of the main post-introduction evaluation strategies identified in the articles was sentinel surveillance, a methodology involving the monitoring of new cases, complications/hospitalizations, and deaths from vaccine-preventable diseases (VPDs) through periodic reports from health services (A1, A2, A3, A8) and/or healthcare professionals (A3, A5, A7). The criteria for sentinel site selection, as well as the frequency and format of reporting, varied across the studies.
One study also reported the use of the Synthetic Control method, which is based on comparing a ‘case’ scenario (the immunization program post-vaccine introduction) with a synthetic control (a potential comparison time series representing the scenario in the absence of, and/or removal of, the vaccine introduction) (A6). Additionally, economic evaluations and comparisons between the pre-introduction scenario (using historical series) and the post-introduction scenario (current data) were also reported (A4).
The WHO post-introduction evaluation tool was used in three studies (A5, A7, A9). Notably, one study employed a mixed-methods approach, adapting both the WHO tool and the Common Review Mission (CRM) of the National Rural Health Mission (NRHM). In this study, field visits were conducted to public and private health facilities, along with interviews with healthcare professionals, policy managers, and caregivers (A5). Particular attention was given to the tool adapted from the WHO New Vaccine Introduction (NVI) checklist (A9).
Notably, the process of introducing vaccines itself served as an opportunity to review immunization policies, train healthcare professionals, and launch new pro-vaccination mobilization and communication campaigns (A3, A5, A7). Challenges to these strategies included issues related to healthcare professionals (A3, A7, A8) and the availability of high-quality vaccination data (A2, A5).
4 Discussion
This systematic literature review examined the key monitoring strategies implemented in various countries following the introduction of new vaccines into national immunization programs. It highlighted the importance of evaluating vaccine safety, coverage, and costs, primarily through national surveillance systems and sentinel surveillance involving direct engagement with health facilities. Post-introduction evaluations offer essential insights for improving existing programs and guiding future vaccine introductions [ 34].
The introduction of new vaccines into immunization programs requires proactive planning, from conception through implementation. It involves both national and international coordination, as well as local and cultural factors that must be understood and taken into account [ 35]. The WHO recommends that all countries introducing a new vaccine assess its impact on public health by conducting a post-introduction evaluation within six to twelve months. Early evaluations may lead to misleading conclusions, particularly in contexts with a low incidence of the target disease or where vaccine coverage is still expanding. Careful assessment of the implementation context is therefore essential [ 36].
Routine surveillance for vaccine-preventable diseases initially developed mainly as a post-introduction activity, with four key objectives: (1) monitor progress toward eradication, elimination, or control; (2) ensure rapid outbreak detection and response; (3) validate vaccination coverage data; and (4) track unforeseen impacts on disease epidemiology (e.g., shifts in age distribution). However, the appropriate surveillance models and strategies for the post-introduction phase remain unclear, as the scope and approach may vary depending on the disease's epidemiological characteristics [ 27].
In 2010, the WHO proposed a post-introduction evaluation (PIE) tool, designed as a comprehensive ‘mini-assessment’ of immunization programs. Since program performance is typically reviewed every three to five years, a more focused evaluation following the introduction of a new vaccine can help identify issues promptly and highlight the strengths of the innovation. Post-introduction evaluations are conducted using questionnaires, standard checklists, direct observation of current practices, and reporting across all levels of the system, including the cold chain and health facilities (vaccine administration sites) [ 36].
Planning is essential for implementing a successful post-introduction evaluation strategy. The WHO tool covers ten key evaluation areas: (1) introduction planning; (2) vaccination coverage, dropout rates, and disease case reporting; (3) cold chain management; (4) vaccine management, transport, and logistics; (5) monitoring and surveillance; (6) health worker training; (7) vaccination safety and waste management; (8) vaccine wastage; (9) adverse events following immunization; and (10) awareness, communication, and acceptance [ 36].
When Ghana introduced the malaria vaccine into its immunization program in 2019, a post-introduction evaluation was conducted in 18 selected districts to assess program implementation and impact. Preparations for the vaccine introduction began ten years before with the formation of a Technical Working Group. The evaluation used the WHO-proposed tool, ultimately rating Ghana's performance in implementing the malaria vaccine as ‘good’. Program objectives, policy, national coordination mechanisms, waste management strategy, health worker training, and pharmacovigilance were identified as strengths, whereas distribution strategies, costs, cold chain management, monitoring and evaluation, advocacy, communication, and social mobilization presented opportunities for improvement [ 34]. Similarly, the Indian states of Tamil Nadu and Kerala applied the WHO-recommended tool in 2012 to assess the impact of introducing the pentavalent vaccine. Positive effects were observed in management (enhanced oversight by policymakers and program coordinators), service delivery (higher vaccination coverage and improved quality of care), and financing (increased resource allocation and reduced direct costs associated with vaccine-preventable diseases [ 30].
The implementation of epidemiological surveillance monitoring programs for vaccine-preventable diseases faces significant challenges in both low-and middle-income countries (LMICs) and high-income countries (HICs), although the reasons are obviously different. In low-income contexts, the difficulties cited are often related to insufficient infrastructure, a shortage of qualified human resources, and fragile health information systems. Limited financial resources compromise the maintenance of efficient registration and notification systems. In addition, dependence on external funding and political instability exacerbate the discontinuity of actions. On the other hand, although they are more technologically advanced, HIC countries express their challenges in a more sociopolitical and behavioral way [ 37], such as vaccine hesitancy, driven by misinformation, anti-vaccine movements, among others [ 38]. These factors have compromised the effectiveness of immunization programs and, consequently, the ability to adequately monitor after the incorporation of new vaccines.
This systematic review found that, in the analyzed studies, sentinel surveillance emerged as one of the main strategies for vaccines post-introduction evaluation. While epidemiological surveillance plays a vital role in supporting comprehensive health care, its scope is often too limited, underscoring the need to strengthen its reach. Effective methods must be feasible for use at the local level, enabling more complete assessments of population health and living conditions. In this approach, hospitals or health facilities specializing in communicable diseases act as ‘sentinel sites,’ providing early warning for investigations and the implementation of disease control measures [ 39]. In 2007, when the WHO updated its position paper on rotavirus vaccines, it recommended establishing a sufficient number of sentinel surveillance sites at national or regional levels before large-scale vaccination program implementation, to generate baseline data representative of severe rotavirus disease incidence [ 40]. In addition to pre-introduction surveillance, it is important to adopt a model for post-introduction impact assessment that is tailored to the clinical and epidemiological characteristics of each disease. For rotavirus, which presents with the non-specific clinical profile of gastroenteritis, aggregated passive syndromic reporting—such as that used for diphtheria, pertussis, or measles—cannot be applied. The very high incidence of diarrhea among children under five years of age, combined with the severely limited laboratory infrastructure in most developing countries, makes surveillance of all cases impractical. Sentinel hospital surveillance—focused on identifying cases among hospitalized children under five in selected hospitals, alongside the regular collection and monitoring of aggregated national data on total hospital admissions—may therefore be the most practical model for routine post-introduction monitoring of the rotavirus vaccine, particularly in developing countries [ 27]. A review that analyzed the nine attributes of surveillance systems according to the Updated Guidelines for the Evaluation of Public Health Surveillance Systems found that 67 % of countries use sentinel surveillance (Ghana, Nigeria, Australia, Indonesia, Ethiopia, and Pakistan) [ 41]. However, it is important to consider both the local context and the particular vaccine being introduced. Countries with robust surveillance systems may not have this approach as their primary strategy.
Economic evaluation plays a key role in monitoring vaccine introduction, as it enables the use of real-world evidence to assess program value. Insights into cost-effectiveness over time can guide decisions on vaccine pricing, improve understanding of uptake, and reduce uncertainty in retrospective analyses—ultimately strengthening the reliability of cost-effectiveness estimates [ 29]. This type of evaluation can also inform future decisions about replacing existing vaccination programs—for instance, introducing pneumococcal conjugate vaccines with broader serotype coverage [ 42–44]. Newall et al. (2014) found that post-introduction economic evaluations of vaccines employed a variety of methodological approaches, underscoring the need for more in-depth research to determine how applying different approaches might influence evaluation outcomes under varying circumstances [ 29].
Vaccines have wide-ranging benefits, but these are often poorly quantified and are not typically involved in discussions of regulatory and implementation policies. The economic value of vaccines has been underestimated using traditional evaluation methods. Modern vaccine cost-benefit studies have gone beyond safety and efficacy to additional impact measures and strategies, which have assessed the reduction in disease burden and inequalities among populations. However, further efforts are still needed to include broader direct and indirect parameters [ 45]. What is generally perceived is that national immunization programs do not have human resources specialized in economics, facing difficulties from this point of view in management.
Finally, one of the studies in this review used the synthetic control method (causal impact) to assess how the introduction of pneumococcal conjugate vaccines affected all-cause pneumonia hospitalizations in five countries in the Americas, including Brazil. This approach may also be useful for strengthening vaccine monitoring studies, as it improves result comparability and precision by constructing a composite of potential comparison time series to generate a counterfactual scenario, which is then evaluated after the intervention [ 31].
Recommendations for post-introduction vaccine monitoring strategies should begin with a thorough assessment of existing systems. This ensures that monitoring becomes not just a one-time exercise, but an integral part of an ongoing process to evaluate and strengthen public immunization policies.
This systematic review has limitations, most notably the small number of studies included. However, the authors conducted searches across multiple databases without restrictions on publication date or language (with the sole exception of one study in Persian, which had to be excluded after exhaustive but unsuccessful attempts at translation). Despite the limited number of studies, this review incorporated articles from low-, middle-, and high-income countries. It also covered vaccines across a range of age groups, rather than focusing exclusively on children. The exclusion of studies that addressed post-incorporation monitoring of COVID-19 vaccines can also be considered a limitation. However, the pandemic constituted an exceptional situation, which makes it impossible to compare it with routine processes observed in relation to other vaccines, especially due to the short interval between licensing and authorization for use in a real-world setting. Measuring the impact of newly introduced vaccines on a product-specific basis and conducting a comprehensive search for effectiveness studies could be the focus of future literature reviews, since these objectives were beyond the scope of the present study. Furthermore, it is noteworthy that most of the included studies were conducted by academic or research institutions rather than immunization programs. Consequently, assessing the programmatic performance and impact of new vaccine introductions was not possible. This underscores the importance of distinguishing routine coverage monitoring and surveillance from tools specifically designed to evaluate the programmatic performance and impact of newly introduced vaccines.
4.1 Final considerations.
This systematic review identified the main strategies for monitoring vaccine introduction in immunization programs worldwide, as reported in the literature: the WHO post-introduction evaluation tool, sentinel surveillance, synthetic controls, economic evaluations, and comparisons between pre- and post-introduction scenarios using historical and current data. Although no standardized approach exists, monitoring can include new case surveillance, disease-related morbidity and mortality, complications and hospitalizations, adverse events, quality of life, vaccine coverage, health professional training, vaccine acceptance, and vaccination logistics.
Post-introduction evaluation strategies included sentinel surveillance, case-control methods, site visits and observations at healthcare facilities, interviews with health professionals, program managers, and caregivers, as well as national surveillance systems, with particular emphasis on the WHO's recommended tool. Beyond their epidemiological significance, the introduction of vaccines into immunization programs provides a valuable opportunity to reassess policies and workflows, enhance professional training, and foster social mobilization in favor of vaccination.
CRediT authorship contribution statement
Ana Catarina de Melo Araújo: Writing – review & editing, Conceptualization. Alice Gomes Frugoli: Writing – review & editing, Writing – original draft, Methodology, Data curation. Jéssica Emanuela de Sena Gonçalves: Writing – review & editing. Jadher Pércio: Writing – review & editing. Thiago Petra Da Silva: Writing – review & editing, Conceptualization. Thayssa Neiva da Fonseca Victer: Writing – review & editing. Fernanda Penido Matozinhos: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Éder Gatti Fernandes: Writing – review & editing, Visualization, Validation, Supervision, Resources.
Funding
This work was supported by the
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We thank the Department of the National Immunization Program (DPNI) and the Observatory for Research and Studies in Vaccination (OPESV – EEUFMG) for their support in carrying out this study.
Appendix A Supplementary data
Supplementary material 1
Supplementary material 2
Supplementary material 3
Appendix A Supplementary data
Supplementary data to this article can be found online at
Table 1
| Identifier | Author and year of publication | Location | Study design | Vaccines covered | Study team/leadership group |
| A1 | Shefer et al., 2008 | United States, Canada, and Australia | Descriptive | Human Papillomavirus (HPV) Vaccine | Federal Public Entity |
| A2 | Rani e Roesel, 2009 | Asian countries (China, Hong Kong, Indonesia, Malaysia, Myanmar, South Korea, Taiwan, Thailand, and Vietnam) | Descriptive | Rotavirus Vaccine | Expanded Immunization Program |
| A3 | Siedler e Arndt, 2010 |
Germany |
Descriptive |
Varicella Vaccine |
Pharmaceutical Industry
Non-Governmental Organization (NGO) Public-private partnership |
| A4 | Newall et al., 2014 | – | Descriptive | – | University
Public hospital |
| A5 | Lahariya et al., 2016 | Tamil Nadu and Kerala (India) | Descriptive | Pentavalent (DPT + HepB + Hib) | Ministry of Health and Family Welfare |
| A6 | Bruhn et al., 2017 | Brazil, Chile, Ecuador, Mexico, and the United States | Coorte | Pneumococcal Conjugate Vaccines | University |
| A7 | Osadebe et al., 2017 | Kano (Nigeria) | Descriptive | Poliomyelitis Vaccine | Federal public entity
Local government |
| A8 | Nair et al., 2019 | India | Descriptive | Rotavirus Vaccine | Federal public entity
Local government |
| A9 | Adjei et al., 2024 |
Ghana |
Transversal |
Malaria Vaccine |
Ministry of Health
Public entity WHO* PATH** UNICEF*** |
Table 2
| ID | Reported strategies | Target population | Costs and required resources | Key outcomes using the strategy | Strategy impediments | Strategy facilitators | Key recommendations based on strategy implementation |
| A1 | National Cancer Registries Program, Epidemiological Surveillance, and National Research: United States
National Immunization Coverage Surveys, comprehensive cancer registries, sentinel surveillance: Canada Vaccination coverage monitoring and population-based studies: Australia |
Girls aged 9 and 11–12 years, and women aged 13–26 years | United States: Funded by both public and private sources.
Canada: Each province/territory independently plans, funds, and delivers programs. Australia: The government funded a two-year catch-up vaccination program. |
Not reported. | Informed consent for vaccinating minors and predictors of vaccine acceptance and refusal. |
Not reported. |
Not reported. |
| A2 | Hospital sentinel surveillance | Hospitalized children under 5 years of age | Not reported. | Establish hospital-based sentinel surveillance as a core part of the broader communicable disease monitoring system | Continuously monitor vaccination programs without ensuring validation of reported coverage or identifying areas with low uptake; In developing countries, infectious disease surveillance often relies on external funding, which may limit its long-term sustainability; Political, programmatic, and technical challenges | Not reported. | The utility of the limited data generated by surveillance in just one or two sentinel hospitals can be substantially enhanced through a supranational surveillance network approach. |
| A3 | Sentinel Surveillance and questionnaires to pediatricians and general practitioners | <1 year old, 1–4 years old, 5–9 years old, 10–14 years old, 20 years old and older | Not reported. | Identification of disease peaks decreased over time; The number of varicella cases reported monthly per unit decreased across all age groups. | Adherence of general practitioners to the vaccination schedule. | Higher adherence among pediatricians; Greater public acceptance of the vaccine; Reimbursement policies, vaccine availability, and vaccination schedule | Hospital-based sentinel surveillance is considered the most feasible option in developing countries for new vaccine-preventable diseases with nonspecific symptoms and high hospitalization rates; Sentinel surveillance is well-suited for generating hypotheses for future investigations. |
| A4 | Retrospective economic evaluations of vaccination programs | Not reported | Not reported | Post-marketing surveillance can be adapted to improve estimates in post-implementation analyses; The strategy can provide insight into the cost–benefit achieved by vaccination programs | Confidentiality of vaccine prices makes it difficult to assess the cost-effectiveness of vaccination programs; Inability to attribute causality to observed declines in disease rates; Post-marketing surveillance is unlikely to detect changes in certain parameters that may be critical for the cost-effectiveness of vaccination programs. | To keep the post-implementation analyses confidential. | Strategies should be adapted based on real-world data. |
| A5 | Post-introduction evaluation (PIE) adapted for India using a ‘mixed-methods approach’.
Data collection: caregivers and private-sector health professionals. Consultation on the approach adopted by the Common Review Mission (CRM) for the National Rural Health Mission (NRHM) in India |
Not reported | Resource development (investments and training); | Increased uptake of public health services by beneficiaries, and improved immunization quality due to workforce retraining; Both states visibly benefited from the vaccine introduction; Revised operational guidelines and training materials; Workforce training, committee restructuring, and improvements in post-vaccination adverse event reporting; Continuous review and enhancement of the cold chain and expansion of sentinel surveillance. | Inconsistent equipment maintenance and vaccine wastage; Challenges in updating records and ensuring consistency in data reporting; Inadequate redistribution of the DTP (diphtheria, tetanus, pertussis) and hepatitis B vaccines immediately after introduction; Difficulty obtaining reports on vaccine coverage, stock levels, and wastage, among other indicators. | High-level political and administrative leadership, enhanced intersectoral coordination, and active engagement of professional associations; Adoption of a multidose vial strategy and enhancement of the surveillance system |
Lessons learned from vaccine introduction can be applied to other health interventions in low- and middle-income countries |
| A6 | Synthetic control method, adapted from Brodersen. | Children under 12 months and adults over 80 years of age. | Not reported. | An average 20 % reduction in pneumonia hospitalizations among infants across five countries. | Synthetic controls are unlikely to eliminate the effects of unmeasured bias and confounding; The impact of the pneumococcal conjugate vaccine may vary between countries due to regional differences. | A promising strategy for adjusting unmeasured bias and confounding in observational studies assessing the impact of public health interventions, enhancing the comparability of such evaluations across different contexts. |
Not reported. |
| A7 |
A routine immunization–specific data module integrated into the National Health Management Information System. Field data collection: WHO Post-Introduction Evaluation (PIE) and Kano quality support supervision tool. |
Children | Not reported | Successful introduction in most areas, facilitated by prior preparatory activities such as updated tools, adequate training, and strong acceptance by both the community and healthcare professional; Comparison of data from the National Health Management Information System with that obtained from primary healthcare units highlights issues of delayed and incomplete reporting; The state of Kano has intensified strategies to improve report timeliness and data quality | Gaps in knowledge regarding multidose vial policy and co-administration; Reluctance among healthcare professionals to administer multiple injectable vaccines in a single visit; Vaccine shortages | The state of Kano intensified strategies to improve reporting timeliness and data quality; Intensive community mobilization; Training and implementation were assessed as successful by participants. | Monitor the impact of these strategies on the improvement of health information delivery and data quality |
| A8 | Active surveillance system | Active surveillance system | Not reported. | Not reported. | Limited space for recording on older vaccination cards; High staff turnover and local inexperience necessitated continuous monitoring of data quality | Potential prior coverage in the private sector with commercial vaccines before official introduction in the public program | Not reported. |
| A9 | Tool adapted from the WHO New Vaccine Introduction (NVI) checklist | Children | No plan was in place to mobilize resources for the malaria vaccine implementation program | Not all health facilities in the implementing districts offered the malaria vaccine; Data collection tools and information systems were reviewed and updated; production of work guides and releases and educational materials. |
Definition of the target population and distribution strategy; financing; vaccine cold chain; monitoring, logistics, and evaluation management; as well as communication, advocacy, and social mobilization activities. |
The structure of the health system contributed to the strengths observed in the introduction of the vaccine; Clear program objectives, well-defined policies, effective national coordination, an appropriate waste management strategy, training of healthcare professionals, and the presence of pharmacovigilance were key factors. | Lessons from the malaria vaccine implementation program may be relevant for new regions introducing the malaria vaccine |
Table 3
| Identifier | Author, Year | Selection (maximum four stars) | Comparability (maximum two stars) | Assessment of the Result (maximum three stars) | Score |
| A1 | Shefer et al., 2008 | **** | * | *** | 8 |
| A2 | Rani e Roesel, 2009 | *** | * | *** | 7 |
| A3 | Siedler e Arndt, 2010 | **** | ** | *** | 9 |
| A4 | Newall et al., 2014 | *** | * | *** | 7 |
| A5 | Lahariya et al., 2016 | *** | * | *** | 7 |
| A6 | Bruhn et al., 2017 | **** | ** | *** | 9 |
| A7 | Osadebe et al., 2017 | **** | ** | *** | 9 |
| A8 | Nair et al., 2019 | *** | ** | ** | 7 |
| A9 | Adjei et al., 2024 | **** | ** | *** | 9 |
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